#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int n = s.size();
/*   for (int i = 0; i < n; i++) {
    if (s[i] < s[i - 1]) {
      cout << "No" << endl;
      return 0;
    }
  } */

  for( int i = 0; i < n - 1; i++) {
    if( s[i] > s[i + 1]) {
        cout << "No" << endl;
        return 0;
    }
  }
  
  cout << "Yes" << endl;

  return 0;
}